Various methods are known for sharing network communication channels or links among stations in a local area network. One widely used method is known as CSMA/CD, (carrier sense multiple access with collision detection). According to this method, a station wishing to transmit a message listens until the transmission channel is idle before commencing to transmit an information packet. Furthermore, the station continues to listen to the channel after commencing a transmission. If a collision is detected, indicating another station has also commenced transmission of an information packet, the station detecting the collision terminates its message transmission and transmits a jam pattern (or garble). In this manner, all other stations are informed of the collision. Once informed, the stations terminate message transmission and wait a random time before attempting to commence a further message transmission.
The CSMA/CD protocol is the subject of an international (ISO) standard and corresponding IEEE Standard, No. 802.3, and has become a generally used protocol for LANs utilizing wired connections for transmission between the stations. In consequence, CSMA/CD LAN controller chips have become widely commercially available. Several manufacturers produce such chips, complying with the IEEE 802.3 standard. An example is the Intel 82586 LAN coprocessor chip, available from Intel Corporation of Santa Clara, Calif., U.S.A. Such chips provide various functions useful in LANs, such as data rate range and backoff algorithm and configurable parameters such as slot time duration, retry counter offset and limit, and interframe spacing time.
A disadvantage of wired LANs is that extensive cabling is required to interconnect the stations. Cabling is generally inconvenient to install and gives rise to inflexibility if it is later desired to alter the physical locations of the stations. It has been proposed to utilize a wireless transmission link operating at radio frequencies to replace the cabling interconnections of a LAN. However, if only a single radio channel is to be utilized for such a LAN, the widely accepted CSMA/CD protocol cannot generally be applied since a station cannot normally receive (or listen) while it is transmitting.
A single radio channel or frequency band is commonly used by multiple LANs. Normally, there is no interference between such LANs if they are sufficiently separated by distance or by a physical barrier such as a wall, floor or building. To increase the coverage area of a LAN, two or more LANs can be linked by a single LAN station which serves as a bridge. The bridging station is provided with a number of antennas, each antenna communicating respectively to a designated LAN. A bridging station can apply an algorithm that learns which signal data transmitted in one LAN is destined to a station on the other LAN. Signal data received by the antenna associated with a first LAN, can be retransmitted via the antenna associated with a second LAN.
As noted, the bridging station has one antenna designated to receive signals from each LAN. Frequently, another (non-designated) antenna of the bridging station will pick up signals intended to be received by the designated antenna. Upon detecting such a signal, the non-designated antenna will temporarily refrain from transmitting to avoid interfering with reception of the designated antenna. However, if the designated antenna receives a weak signal from its LAN, then the non-designated antenna might not detect that signal at all. If the non-designated antenna does not detect the signal, it may assume that it is free to commence a transmission. However, if one antenna starts to transmit when the other is receiving data, the transmitted signal can easily interfere with reception on the other antenna. Such interference is the problem the present invention addresses.